This invention relates generally to a semiconductor integrated circuit (IC) device. More particularly, the present invention relates to semiconductor circuit technique which is effective when applied, for example, to a semiconductor memory device incorporating therein a substrate bias generation circuit such as a dynamic RAM (Random Access Memory).
In semiconductor memory devices constituted by MOSFETs (Insulated Gate type Field Effect Transistors), it is known in the art to generate a substrate back-bias voltage by a built-in substrate back-bias generation circuit in order to reduce the parasitic capacitance between circuit elements such as MOSFETs and a semiconductor substrate in which the MOSFETs are formed. (For example, refer to "Nikkei Electronics", May 14, 1979, p.p. 77-79, published by Nikkei McGraw Hill Co.) When such a substrate bias generation circuit is incorporated, a power source voltage to be supplied to a semiconductor memory device can be unified to a voltage such as 5 V, and the number of external terminals therefor can be reduced.
As a result of studies, however, the inventors of the present invention have found that if a circuit for rectifying the output pulses generated continuously by an oscillation circuit is used in this case, the following problem develops. A current flowing to the substrate varies greatly between the accessing state in which each circuit starts operating simultaneously and the non-accessing state in which no internal circuit operates. Therefore, when the substrate back-bias voltage is generated by rectifying those oscillation pulses that are generated in no relation to circuit operation, the current supply capacity is essentially set in a "worst case" condition. This requires relatively large capacitor and rectification elements and a driving circuit, so that the integration density of the semiconductor integrated circuit is reduced. In addition, more current is drawn. (For details of the substrate bias generation circuit, refer to Japanese Patent Laid-Open No. 13566/1980, for example).